Disproportionation of toluene



Nov. 14, 1961 Filed Oct. l1. 1960 SETTLEH- SEPARTO/i' S. D. LEVY ETAL DISPROPORTIONATION OF' TOLUENE 2 Sheets-Shea?I 1 ATTORNEY Nov. 14, 196.1 s D, LEVY ETAL 3,009,004

DISPROPORTIONATION OF TOLUENE Siep/Ien D. Levy David A. McCall/ay Ri ham' .l Mikal/sk By m@ AT OR/VEY carbon.

United States Patent O 3,009,004 DISPROPORTIONATION F TOLUENE Stephen D. Levy, Salk Village, David A. McCaulay,

Homewood, and Richard J. Mikovsky, Park Forest, Ill., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Filed Oct. V11, 1960, Ser. No. 61,909 15 Claims. (Cl. 260--672) This invention relates to a process for the disproportionation of toluene to produce benzene and polymethyl benzene. More particularly, this invention is concerned with a process employing a Ireaction promoter in the conversion of toluene to benzene and xylene and/ or other polymethyl benzenes. It is known in the art that certain alkyl benzenes, other than toluene, can be disproportio-nated with a BF3 catalyst in the presence of HF. For example, A. P. Lien et al., U.S. 2,528,893, patented November 7, 1950, discloses a method yfor the disproportionation of ethyl benzene to diet-hylbenzene and benzene in good yields. Also, A. P. Lien et al., U.S. 2,564,073, patented August 14, 1951, discloses the disproportionation of xylene to trimet-hyl benzene in good yields. However, it had previously been thought impossible to disproportionate toluene -in .good yields until recently. Toluene contains only one alkyl group on the aromatic nucleus and the alkyl group is a methyl group. It is extremely difficult to remove the methyl group from the toluene nucleus and place it on the aromatic nucleus of another toluene molecule by disproportionation.

However, a process has been developed for disproportionating toluene and obtaining good yield of xylene and other polymethyl benzenes without undue destruction of the reaction product by cracking and condensation. The I recently developed process uses an HF-.-BF3 catalyst and reaction temperatures of from 80 C. to 125 C. Although good yields of polymethyl benzenes, such as xylene and mesitylene, are obtained ,from the process, the process is useful on a commercial basis only over a limited temperature range and only with a particular catalyst.

We have now discovered that the disproportionation of toluene to benzene and polymethyl benzene can be carried out over a Iwider temperature range while using any strong acid Friedel-Crafts catalyst by using certain promoters for the disproportionation reaction. Accordingly, toluene is contacted with a strong acid Friedel- Crafts catalyst at a temperature in the range of from yabout 0 C. to 125 C. in the presence of a promoter selected from the class consisting of a diarylmethane having mononuclear aryl groups and a polyhalohydro- The polyhalohydrocarbon which is useable as a promoter has the gem-dihalo structure yand corresponds to the following structural formula:

Red-B' wherein X is a halo group and R and R are each selected from the class .consisting of Ya holo group, a hydrogen group, an alkyl group and a hydrogen-.containing haloal'kyl group. The halo groups may be uoro, chloro, bromo and/or iodo groups. The hydrogen-containing haloalkyl group may advantageously be an open'chain (i.e., nonfcyclic) alkyl group yalthough it may contain vroyolopsratlno or aromatic substituents ills alkyl group and haloalkyl group are preferably saturated. The contacting is carried out for a period yof time gsuicient to disproportionate toluene to the desired polymethylgbenzene, and the polymethylbenzene `is then separated from ICC the reacted mixture as a disproportionation product. Benzene may also be separated as a product if desired. Any remaining unreacted toluene may be recycled to the contacting step.

It is preferred that the promoter be readily separable from the desired reaction product, such als by distilla-V tion. Therefore, in an advantageous embodiment of this invention, the promoter lboils outside the boiling range of desired products. l

The diarylmethane and polyhalohydrocarbon promoters useable in accordance .herewithare at least partially soluble in the catalyst phase or in the toluene Phase or lboth phases under the reaction conditions. Complete solubility is desirable lfor greater promoter activity but -is not necessary. Where the promoters are referred to herein as being soluble or partially soluble, it is fully intended that they may be onlyy Very slightlyv soluble so long as they possess some solubility in the reaction system.

The diarylmethanes are those diarylmethanes wherein the aryl groups are mononuclear aromatic groups and are capable of splitting off a phenyl nucleus' (including alkyl substituted phenyl nuclei) and -a benzylV ion (including alkyl substituted benzyl ions). Thus, any arylmethane wherein the aryl group is a benzene group or an alkylbenzene group ,is useful. Specific examples of such diarylmethanes are ditoluomethane, diphenylrnethane, dixylomethane, dimesitylmethane, ethylphenyltoluomethane, di(ethylphenyl)methane, di(octylphenyl)rnethane, di(butylphenyl)methane, eicosphenyltoluomethane, di- (octyldecylphenyl)methane, h e x adecylphenylxylomethane, and the like. Diphenylmethane is particularly pre ferred.

The polyhalohydrocarbons useable as promoters have been defined with reference to the above formula. v From the formula, it is evident that the polyha'lohydrocarbon promoters must containa-t least two halogen groups on the same carbon atoms, li.e. a gem-dithalo structure. It is lalso evident that, although the term polyhalohydrocarbon is used in the general description of the compound within the formula, it is not necessary that hydrogen be present in the compound where there -is only one carbon atom .in tho tomula- Thus. such v.ootnrroiltlts ,as Carbon totrsohloride, oarbon totrabroraido. oar-bootstrauoride, and the Freons are useable. The Freons Linclude IFreon lil (CC13F), Freon 12 (Q Clglg) and LFE-Q11 13 (CClFg). However, with reference tothe structural formula, where more than one carbon atom is present the promoter Iis not ,a perhalo compound, i,e. it ,contains hydrogen linked to a .carbon atom.

Tho polyhalohydrooarbon ymay be of any molecular Weight desirod- The polyhalohydrooavbon vis preferably a saturated open chain'polyhalohydrocarbon of'anyohain length `desired with respect to the solubility or partial solubility in the reactants as Vdisclosed above. The polyhalohydrocarbon may have as many halogen groups and/ or gem-dihalo structures as desired so long as it has .at .losst one gom-dihslo structure and, whore the poly- 'holohydrooarbon has moro than one .carbon atom, .at

least ons hydrogen group as dosor-ibod ,abovepro- `ferred halogen of the gemdihalo structure is chlorine. Typioal ots-amples of other spooio useable 4atalyhalshydrocarbons are promoters are 1,1,l-trichloro-Z-phenylethane;

1,1,1,2-tetrachloroethane; 1,1,2,2-tetrabromoethane; 1,1-diidopropane;

pentachloroethane; 2,2-dibromobutane; 1,l-diodo-Z-iodo-2-methylpropane; l-chloro-l-iodopentane; 1,1,2,2,3,3,4,4octachlorobutane; 3,3diodo-2-methylbutane; 1,1-dibromo-Z-methylbutane; l,1-dichloro-2,Z-dimethylpropane; 1,4-dichloro-1,4-dibromobutane; 1,1-diuorohexane; 1,6-dichloro-1,6-dibromo-1-iodohexane; chlorobromomethane; 1,1,3-trilluoropropane;

1 1-diuoro-2,2dimethylpropane; .1,1,2-trichloro-l,2-diuoroethane; dibromomethane;

1, l-dichloro-2-methyl-3 -methylhexaneg octadecailuorononane; hexachloropropane; l,1,10,|lO-tetrauorodecane; 1,1,3-trich1oro-2-(chloromethyl) propane; 1 ,1,1-tri-bromododecane; diidomethane;

.trichloroethylene;

2,2-diiluoropropane; 2,2-dichlorooctane; l3,3-dichloro-2,2,4-trimethylpentane;

v1,1-diiodoeicosar1e;

1,1,8,8tetrauoro-3,3,5,5-tetraethyloctane;

l-chloro-l,l-dibromooctadecane; .3,3 ,4,4,4pentachloro2metbylbutane; 1,1 ,1,2,2-pentachlorohexane;

1,l,12,12-1auryltetrach1oride;

palmityloctafluoride',

lhexachlorobutadiene;

propylpentaiodide; 1,3 ,4,4-tetrachlorobutene-1 13,3,6-trichlorohexadiene-1,4;

hexadecyldecachloride, etc.

Also useable are the halogenated hydrocarbons such "as halogenated waxes and halogenated hydrocarbon polymers, e.'g. chlorinated paratiin waxes, such as those containing from 30 to 70 weight percent chlorine and marketed under such trade names as Aroclor (Monsanto Chemical Co); Chlorowax 40 and 70 (Diamond Alkali Co.); Cloran 42 and 70 (Hercules Powder 0o.); CP-40 (Hooker Electrochemical Co.); Halowax (Union Carbide `8: Carbon Corp.); Paroil (Amoco Chemicals, Inc), etc.,

`ene; iodinated polyisobutylene; brominated paraffin wax; iluorinated Aolefin waxes, etc.

Further, the polyhalohydrocarbon may be a chlorine-containing polymer such as .polyvinylidinechloride Examples of additional useable l-naphthenyl-12,12-dibromododecane; chlorinated hydrocarbon petroleum fractions such as the chlorinated naphthalenes, and the like. Other polyhalohydrocarbons falling within the above definition are well known to those skilled in the art and any such compositions may be used. Where it is desired to use a viscous polyhalohydroca-rbon, it may be particularly desirable to mix the Viscous polyhalohydrocarbon with a low molecular weight polyhalohydrocarbon which functions not only as an additional promoter but also as a solvent for the more viscous material. The polyhalohydrocarbon is soluble in toluene or the catalyst phase or may be rendered soluble in toluene or the catalyst phase by solvents.

ously, the contacting temperature is lower than aboutl C., because above 100 C. advantageous commercial processing may be obtained using the I-IF-BF3 catalyst in accordance with the method of D. A. McCaulay described in copending application Serial No. 51,223. The reaction temperature also depends upon the particular promoter used. Accordingly, where the polyhalohydro carbon is used as a promoter, it may be advantageous to use temperatures in the range of from 50 to 100 C. and, preferably 65 to 100 C. Where a diarylmethane is used as the promoter, the preferred temperature range is 20 to 75 C. The contacting is carried out for a period of time sufficient to produce the desired product. Usually from about 15 minutes to about 5 hours may be required. However, at lower temperatures the reaction times will be longer and conversely at higher reaction temperatures less reaction time will be required. The reaction time should be related to reaction temperature and catalyst to obtain the desired conversion to the desired product and to minimize side reactions. The promoter used will aect reaction times and suitable reaction time can readily be determined by simple experimentationV within the skill of the art.

The reaction in the presence of the catalyst is believed to be promoted by the presence of either the gem-dihalo carbon group or the phenyl nucleus and benzyl ion when utilizing the promoters of this invention.`

The strong acid Friedel-Crafts catalysts are well known to the art and any such catalyst may be used in the present reaction. Particularly advantageous catalysts are those very strong acid Friedel-Crafts catalysts such as HF-BF3; AlClg-HCl; AlBr3-HBr, and the like. The catalyst is used in a catalytically eifective amount. Advantageously, the amount of catalyst employed may be in the range of from about 0.1 to about 3.0 parts by weight of catalyst per part by weight of toluene. Where the catalyst includes an additional promoter -such as HF; HCl, and HBr, the hydrogen halide should also be used in an amount from about 0.1 to about 3.0 parts by weight per part of toluene. Of course, the amount of catalyst used will depend somewhat upon the nature of the catalyst. For example, where HF--B-F3 is used, it is advantageous to employ at least about 0.3 Weight percent of each of HF and BF3. As another example, where an aluminum halide-hydrogen halide catalyst is employed, the amount used for an equivalent amount of disproportionation may be at little' as 0.1 weight percent of each of the aluminum halide and hydrogen halide. It is particularly preferred that at least 0.5 weight percent of the catalyst be used for eicient commercial operation. HF- BF3 is the preferred catalyst.

In the process of this invention, the contacting in the presence of the strong acid Friedel-Crafts catalyst and promoter may be carried out atv any pressure normally used for the particular catalyst system. Where a catalyst system containing a hydrogen halide is used, it is normally advantageous to carry the contacting out while maintaining hydrogen halide in liquid phase. Where HC1 or HBr are used in the catalyst system, the hydrogenhalide may advantageously be dissolved in the reactants, eg. in the toluene, and additional pressure is not necessary. HC1 or HBr may also be present in the gaseous'state as undissolved gas. However, Where IdF-EP3, the preferred catalyst system, is used, the contacting must be carried out under pressures suflicient to maintain the HF in the liquid state.

After contacting, the product may be `fractionated to provide benzene and polymethylbenzenes which are removed from the system. Fractionation of the product may also yield unconverted toluene which may be recycled to the contacting step. The catalyst may be removed during fractionation and recycled and reused. The polyhalohydrocarbon or diarylmethane promoter may also be separated by fractionation and recycled to the contacting step. Fractionation of the product or eiluent from the contacting step may conveniently be accomplished by distillation whereby separate benzene, toluene and polymethylbenzene fractions are recovered. Any hydrogen 6 covered through line 21 and charged to fractionator 22. In fractionator 22, the stripped bottoms are distilled to obtain a light benzene reaction through line 23, an inter mediate toluene fraction through line 24, an intermediate halide promoter may be recovered as overhead from the Xylene fraction through line 25, an intermediate mesitylene distillation, as may BFa when BF3 is contained in the fraction through line 27 and a bottoms fraction through catalyst system. The lower molecular weight polyhaloline 28. The benzene reaction lrecovered through line 23 hydrocarbon promoters may berecovered as a low-boiling is a high-purity product and may be removed from the fraction ffrom the distillation and recycled while the disystem. The toluene fraction is recycled lthrough line 24 .arylmethane or high-boiling polyhalohydrocarbons and 10 to line 13 and commingled with additional toluene charged catalysts other than BF3 may be recovered and recycled through contactor -17. The xyl-ene and mesitylene fracas bottoms from distillation. tions are recovered las separate products. The bottoms The polymethylbenzene recovered as product from the fraction contains diphenylmethane and polymethylbensystem may conveniently be preselected. Increased rezenes heavier than mesitylene and may be either recycled action temperatures and reaction times are then used to through line 24 or removed from the system through yield a polymethylbenzene having a greater number of valved line 30. The bottoms fraction recovered through polymethyl groups. F01' @I ample, 10WefC0I1taCtiI1gtem fline 28 may also contain condensation products of diperatures and contacting tlmes are used for production phenylmethane which may be recycled to contactor 17 0f a Pl'CduCt pfedominatllg in Xylelle than are Used, Other and may provide additional promotion of the disproporconditions being constant, for the production of mesityl- 20 tionation reaction within contactor 17. ene. More highly methylated benzenes such as durene EXAMPLES and pentamethylbenzene may also be produced at still longer reaction times and/ or higher temperatures. How- In order to further illustrate the process of this invenever, care should be taken not to exceed 125 C. as a tion, various disproportionation runs were made using reaction temperature because of the tendency toward promoters within the scope of this invention in the disproproduct condensation and formation of tars at such portionation of toluene. The promoter used, amount of higher temperatures. promoter, amount of toluene, amount of catalyst, and FIGURE I is a tlow diagram illustrating the operation conditions of reaction are set out in the following table. of one embodiment of this invention. FIGURE II 4is a At intermittent reaction times identified in the table, semi-log plot of conversion against reaction time using portions ofthe reactants were removed and analyzed with various promoters in accordance herewith. the product composition results reported in the table.

Now turning to FIGURE I, toluene is charged through The conditions and results were as follows:

Table DISPROPORTIONATION 0F TOLUENE Run No 1 2 3 4 5 Toluene Feed, g 61. 5 64. 5 83 98 79 Promoter Identity-. Diphenyl methane None CHaCGIa None Carbon Tetrachlorlde Promoter Amount, g.-- 3.5 None 5 None 4 Catalyst, g.:

HF 75 75 50 50 56 t BFS 61 70 55 57 58 Total Pressure, p.s.i.g.- 500 500 (2) (2) 800 Temperature, O 23 23 65 65 65 Reaction Time, M1n--.- 31 70 133 1,175 6o 3, 923 70 255 415 4a s1 155 1,109 30 90 166 241 39s 1.260 Product Composition,

Mola percent: l

6 7 7 13.8 0.1 1.5 3 12 16 0.3 0.9 1.9 17 1.5 5.0 10.8 14.1 16,2 23.0 ss s6 36 75.6 99.9 97.0 94 76 67 99.4 98.2 96.2 66 97 87.5 76.4 69 64.2 56.4 6 7 7 10.8 0.0 1.5 3 12 16 0.a 0.9 1.9 17 1.5 7.5 12.3 16.9 19.7 26.6

l Adjusted product analysis showing product composition on a promoter-free basis.

I HF maintained in liquid state.

line 13 to contactor 17. Contactor 17 is a contacting vessel equipped with an agitator. BF3; HF and diphenylmethane are charged to line 13 by way of valved 'lines 11, 12, and 14 respectively. 'Ihe catalyst and promoter are then charged to contactor 17 and agitated with the toluene at a temperature of about C. for a period of about three hours.` The concentration of diphenylmethane is about 5% based on toluene and the amount of each of BF3 and HF charged is about two pounds per pound of toluene. After` three hours of contacting, the contents of contactor 17 are removed through line 18 and charged to stripping tower 20. The stripping tower is operated just below the benzene boiling point and HF and BF3 along with some benzene are taken overhead through line 31, cooled in condenser 32 and charged to settler-separator 33. In settler-separator 33, benzene and HF are recovered in the liquid state, through lines 34 and 37 respectively. The recovered benzene is a highpurity benzene product. The liquid HF is recycled through line 37 to line 35 and may be recharged through line 13 to contactor 17. BFS is taken as a gaseous overhead from settler-separator 33 and recycled through line 35 and 13 to contactor 17.

The bottoms fraction from stripping tower 20 is re- With reference to the data reported above in the table, it is seen that the diphenyhnethane, trichloroethane and carbon tetrachloride were elective promoters in thedisproportionation reaction. By comparing the results of runs l and 2, it is seen thatthe diphenylmethane markedly increased the amount of disporportionation in a given length of time. The same is true :for the trichloroethane and carbon tetrachloride, i.e. by comparing the results of runs 3 and 5 with the results of run 4.

Now with reference to FIGURE II, FIGURE II is a semi-log plot of conversion against reaction time. Diphenylmethane, at room temperature, gives an initial 500- fold increase in rate and, although the rate decreases after about '15% conversion, the conversion is still about 15 times higher than the unpromoted disproportionation (too slow to be represented by a curve on the graph). Also with reference to FIGURE II, at 65 C. carbon tetrachloride and trichloroethane gave a 5fold and 3-fold increase respectively in rate over the unpromoted reaction (plotted at 65 C. `as a dotted line).

It is evident from the foregoing that we have provided a promoted disproportionation process which gives increased conversion of toluene to benzene and polymethylbenzenes by utilizing a promoter las herein defined.

We claim:

1. A process for the disproportionation of toluene to produce benzene and a polymethylbenzene, which process comprises contacting toluene at a temperature in the range of from about C. to about 125 C. with a catalytic amount of a strong acid Friedel-Crafts catalyst in the presence of a disproportionation promoter selected Ifrom the class consisting of a diarylmethane having mononuclear aryl groups and a polyhalohydrocarbon having a gemdihalo structure and deiined by the formula:

wherein X is a halogen group and R and R are each selected from the class consisting of a halogen group, a hydrogen group, an alkyl group, and a hydrogen-containing haloalkyl group, said contacting being for a period of time sufficient to disproportionate toluene into said benzene and polymethylbenzene, .and separating said polymethylbenzene as a disproportionation product.

2. The process of claim 1 wherein said disproportionation promoter is present in the reaction mixture in an amount of from about one to about 10% by weight based on said toluene.

3. The process of claim 1 wherein said Friedel-Crafts catalyst is PIF-BFS.

4. The process of claim 3 wherein said catalytic amount is from about 0.3 to about 3.0 parts BF3 and from about 0.2 to about 3.0 parts H'F per part by weight of the toluene to be disproportionated.

5 The process of claim l wherein the contacting temperature is in the range of from about 0 to about 100 C.

6. The process of claim l wherein X is a chlorine group.

7. The process of claim l wherein said disproportionation promoter is a saturated open chain polyhalohydrocarbon boiling outside the benzene `to said polymethylbenzene boiling range.

8. The process of claim 7 wherein said promoter is carbon tetrachloride and the contacting temperature is in the range of from about 50 to about 100 C.

9. The process of claim 7 wherein said disproportionation promoter is trichloroethane and the contacting temperature is in the range .of from about 50 to about 100 C.

l0. The process of claim 1 wherein said disproportionation promoter is a diarylmethane boiling above mesitylene.

l1. The process of claim 10 wherein said promoter is diphenylmethane and the contacting temperature is in the range of from about to about 75 C.

l2. lA process for disproportionating toluene to form benzene and polymethylbenzenes as disproportionation products, which process comprises contacting toluene at a temperature in the range of from about 0 to about 125 C. with a catalytic amount of a strong acid Friedel- Crafts catalyst in the presence of a promoter selected from the class consisting of a diarylmethane having mono- 8 nuclear aryl groups and a saturated open chain polyhalohydrocarbon dened by the formula:

wherein X is a halogen group and R and R are each selected from the class yconsisting of a Vhalogen group, a hydrogen group, a saturated open chain alkyl group and a hydrogen-containing saturated open chain haloalkyl group, said contacting being conducted .for aperiod of time sucient to disproportionate toluene to benzene and said polymethylbenzene, removing ...said catalyst Vthe resulting contacted mixture, recycling 4said catalyst to ysaid contacting step, recovering benzene and said polymethylbenzene as separate fractions trom said contacted mixture, recovering toluene and said disproportionation promoter from said contacted mixture and recycling recovered toluene and promoter tothe contacting step.

13. A process for the disproportionation of toluene to produce benzene, xylene and mesitylene, Which process comprises contacting toluene at a temperature in the range of from about 20 C. to about 75 C. with an HF--BF3 catalyst and from 1 to 10% diphenylmethane based on said toluene for a period of time sufficient to convert tolueney to benzene, Xylene and mesitylene, stripping HF and BFS from the converted mixture, recycling HF and BF3 to the contacting step, distilling the stripped converted mixture to obtain a high-purity benzene product cut, a toluene cut, a high purity xylene product cut, a high purity mesitylene product cut, and a bottoms fraction containing diphenylmethane, and recycling said toluene cut and said bottoms fraction to said contacting step.

14. A process for the disprop'ortionation of toluene to produce benzene and a polymethylbenzene, which process comprises contacting toluene at a temperature in the range of from about 0 C. to about 125 C. with .a catalytic amount of a strong acid Friedel-Crafts catalyst in the presence of a phenyl nucleus and =a benzyl ion for a period of time sucient to disproportionate toluene into said benzene and polymethylbenzene andseparating lsaid polymethylbenzene as a disproportionation product.

15. A process for the disproportionation of toluene to produce benzene land a polymethylbenzene, which process comprises contacting toluene :at a temperature in the range of from about 0 C. to about 125 C. with .a catalytic amountof a strong acid Friedel-Crafts catalyst in the presence of a gem-dihalo carbon group attached to two Igroups each selected from the, class consisting of a halogen group, a hydrogen group, an alkyl group, and a hydrogen-containing haloalkyl group for a period of time sufficient to `disproportionate toluene into said benzenev and polymethylbenzene and separating said polymethylbenzene as a disproportionation product.

No references. cited. 

1. A PROCESS FOR THE DISPROPORTIONATION OF TOLUENE TO PRODUCE BENZENE AND A POLYMETHYLBENZENE, WHICH PROCESS COMPRISES CONTACTING TOLUENE AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0*C. TO ABOUT 125*C. WITH A CATALYTIC AMOUNT OF A STRONG ACID FRIEDEL-CRAFTS CATALYST IN THE PRESENCE OF A DISPROPORTIONATION PROMOTER SELECTED FROM THE CLASS CONSISTING OF A DIARYLMETHANE HAVING MONONUCLEAR ARYL GROUPS AND A POLYHALOHYDROCARBON HAVING A GEMDIHALO STRUCTURE AND DEFINED BY THE FORMULA: 